For our simple example, assume you have a program named check
that takes two options:
A list of directories to check over for whatever it is check does.
You want this option available as a POSIX-style flag option
and a GNU long option. You want to allow as many of these
as the user wishes.
An option to show or not show the definition tree being used.
Only one occurrence is to be allowed, specifying one or the other.